TWI696712B - Medium-entropy multifunctional super austenitic stainless steel and method of fabricating the same - Google Patents

Abstract

The invention discloses a medium-entropy multifunctional super-austenitic stainless steel and a method of fabricating the same. The medium-entropy multifunctional super-austenitic stainless steel of the invention has a composition including of up to 0.02 wt.% carbon, 20.0~25.0 wt.% chromium, 20.0~25.0 wt.% nickel, 4.0~6.0 wt.% molybdenum, 0.0-5.0 wt.% tungsten, 3.5~5.0 wt.% copper, 0.0~1.0 wt.% manganese, 0.2~0.3 wt.% silicon, 0.2~0.5 wt.% nitrogen, a balance of iron and inevitable impurities. After an aging process, the medium-entropy multifunctional super-austenitic stainless steel of the invention has a plurality of Cu-rich precipitates with a sizes in a range of 2-5 nm.

Description

Medium-entropy multi-function super Vostian iron series stainless steel and Its manufacturing method

The present invention relates to a super stainless steel and a manufacturing method thereof, and particularly relates to a medium entropy multi-functional super Vostian iron-based stainless steel designed based on a medium-entropy alloy and having excellent machinability, mechanical properties, corrosion resistance, and antibacterial properties And its manufacturing method.

The application fields of steel are quite extensive, for example, the automobile, tools, machinery, underwater pipelines and other industrial fields must use a lot of steel. Therefore, the strength and machinability of steel also need to be adjusted to meet different needs in various fields. Compared with other fields, super stainless steel cold-rolled steel sheets with ultra-high corrosion resistance require more complicated heat treatment and processing processes in the production process. Therefore, in addition to the strength requirements, super stainless steel cold-rolled steel sheets with ultra-high corrosion resistance also have specifications for their processing properties, corrosion resistance, antibacterial properties, etc., making Super Vostian iron-based stainless steel steel the current One of the goals for the development of the steel industry.

Regarding the prior art of Super Vostian iron series stainless steel, there has been an application case number of the Patent Cooperation Treaty WO2003044238A1 teaches that the balance of the composition of Super Vostian iron-based stainless steel alloys enables alloys and products made of alloys to meet the requirements of high corrosion resistance, especially in inorganic, organic acids and their mixtures. The Super Vostian iron series stainless steel has excellent general corrosion resistance, excellent structural stability, improved mechanical properties, and excellent machinability, especially in the specific environment in which pipes can be used. The Super Vostian iron-based stainless steel composition contains 23.0~30.0wt.% chromium, 25.0~35.0wt.% nickel, 2.0~6.0wt.% molybdenum, 1.0~6.0wt.% manganese, 0~0.4wt.% nitrogen, Up to 0.05wt.% carbon, up to 1.0wt.% silicon, up to 0.02wt.% sulfur, up to 3.0wt.% copper, 0~6.0wt.% tungsten, up to 2.0wt.% by Mg, Ce , Ca, B, La, Pr, Zr, Ti, Nd, one or more elements in the group, and a balanced amount of iron with the usual impurities and steel-making additives. However, the workability, mechanical properties, and corrosion resistance of this Super Vostian iron-based stainless steel still have a lot of room for improvement, and it does not have an antibacterial effect.

In addition, WO2003044238A1 patent publication teaches that the combination of a high content of copper and a high content of manganese obviously deteriorates the hot ductility. For this reason, the upper limit of the copper content determined is 3.0 weight percent. Obviously, WO2003044238A1 patent publication discloses a Super Vostian iron-based stainless steel system suitable for hot rolling processing, and its upper limit of copper content is 3.0 weight percent. However, the Super Vostian iron-based stainless steel system of the present invention is suitable for cold rolling at room temperature, which can greatly reduce the energy consumed during processing. Also, the present invention The design of the Super Vostian iron series stainless steel alloy needs to have antibacterial effect. Its copper content is higher than 3.0 weight percent, but it still has excellent machinability, mechanical properties, corrosion resistance, and antibacterial properties.

Another prior art of Super Vostian iron-based stainless steel, US Patent Publication No. 20130156628 reveals that the alloy composition contains up to 0.2%wt. carbon, up to 20wt.% manganese, 0.1~1.0wt.% silicon, 14.0~28.0 wt.% chromium, 15.0~38.0wt.% nickel, 2.0~9.0wt.% molybdenum, 0.1~3.0wt.% copper, 0.08~0.9wt.% nitrogen, 0.1~5.0wt.% tungsten, 0.5~5.0wt. % Cobalt, up to 1.0 wt.% titanium, up to 0.05 wt.% boron, up to 0.05 wt.% phosphorus, up to 0.05 wt.% sulfur, and a balanced amount of iron and its accompanying impurities. U.S. Patent Publication No. 20130156628 discloses a super-Wustfield iron-based stainless steel suitable for processing as a drill string assembly used in oil and gas drilling operations. The drill string assembly can withstand impact, wear, friction, heat, loss, erosion, corrosion, and/or deposition. However, in the same way, the workability, mechanical properties, and corrosion resistance of the Super Vostian iron-based stainless steel disclosed in US Patent Publication No. 20130156628 still have a lot of room for improvement, and it does not have an antibacterial effect. And it must be emphasized that the Super Vostian iron-based stainless steel disclosed in US Patent Publication No. 20130156628 also has a copper content of less than 3.0 wt.%.

In addition, because the alloy design considerations of the Super Vostian iron-based stainless steel of the present invention are suitable for cold rolling at room temperature, the behavior and mechanism of processing strain hardening are different from those of the prior art. This technical feature will be described in detail below.

Therefore, one technical problem to be solved by the present invention is to provide a medium-entropy multifunctional super Vostian iron-based stainless steel and a manufacturing method thereof. According to the present invention, the entropy multifunctional super Vostian iron series stainless steel has excellent machinability, mechanical properties, corrosion resistance, and antibacterial properties.

According to one of the preferred embodiments of the present invention, the entropy multifunctional super Vostian iron-based stainless steel contains ingredients up to 0.02wt.% carbon, 20.0-25.0wt.% chromium, 20.0-25.0wt.% nickel, 4.0 ~6.0wt.% molybdenum, 0.0~5.0wt.% tungsten, 3.5~5.0wt.% copper, 0.0~1.0wt.% manganese, 0.2~0.3wt.% silicon, 0.3~0.5wt.% nitrogen, balance Iron and insignificant impurities.

According to a preferred embodiment of the present invention, a method for manufacturing a medium-entropy multi-functional super Vostian iron-based stainless steel, first of all, prepare a raw material whose composition contains up to 0.02wt.% carbon, 20.0~25.0wt.% chromium, 20.0 ~25.0wt.% nickel, 4.0~6.0wt.% molybdenum, 0.0~5.0wt.% tungsten, 3.5~5.0wt.% copper, 0.0~1.0wt.% manganese, 0.2~0.3wt.% silicon, 0.3~0.5 wt.% nitrogen, balanced amount of iron, and insignificant impurities. Next, according to the method of the present invention, the raw material is subjected to a vacuum melting process to obtain a stainless steel with medium entropy and multi-functional super-Wastefield iron stainless steel. Next, the method according to the invention cools the stainless steel material. Finally, the method according to the present invention performs a homogenization process on stainless steel ingots, so that the microstructure of the stainless steel steel is Vostian Iron The phase has a single-phase structure and no hard and brittle sigma phase remains.

Further, according to the method of the present invention, at least one cold rolling process is performed on the stainless steel steel material at room temperature to obtain the finished steel material. Next, the method according to the present invention performs an annealing process on the finished rolled steel material, so that the finished rolled steel material has a grain size range of 19-320 μm.

In a specific embodiment, at least one cold rolling rolling process can cold-roll stainless steel up to 80%.

Further, according to the method of the present invention, an aging treatment process is performed on the finished rolled steel, resulting in precipitation of multiple copper-rich precipitates in the finished rolled steel. The particle size range of multiple copper-rich precipitates is 2~5nm.

Different from the prior art, according to the present invention, the entropy multi-functional super Vostian iron-based stainless steel has a copper content higher than 3.0 wt.%, and has excellent machinability, mechanical properties, corrosion resistance, and antibacterial properties.

The advantages and spirit of the present invention can be further understood through the following detailed description of the invention and the accompanying drawings.

Fig. 1 is the phase balance diagram of the Super Vostian iron series stainless steel calculated by the thermodynamic analysis software-Thermal Calc simulation software.

FIG. 2 is a flowchart of smelting and subsequent processing and heat treatment performed according to the method of the present invention.

FIG. 3 is a metallographic photograph of the entropy multifunctional super Vostian iron-based stainless steel obtained by performing the vacuum smelting process of the method of the present invention and without homogenization, and the composition analysis results of the residual sigma phase.

FIG. 4 is an X-ray diffraction pattern analysis result of the stainless steel material of the entropy multifunctional super Vostian iron series stainless steel in the present invention after homogenization.

FIG. 5 is an X-ray diffraction pattern analysis result of the entropy multifunctional super Vostian iron-based stainless steel in the present invention after homogenization, after cold rolling and annealing at 950° C. for one hour.

FIG. 6 is an image photograph of the entropy multifunctional super Vostian iron-based stainless steel in the present invention after homogenization, cold rolling and annealing, and annealing at 1000° C. for one hour.

FIG. 7 is an image photograph of the entropy multifunctional super Vostian iron-based stainless steel material homogenized, cold-rolled and annealed at 1200° C. and observed by EBSD.

FIG. 8 is a graph showing the relationship between the grain size and hardness of the entropy multi-functional super Vostian iron-based stainless steel in the present invention after different annealing temperatures and times.

Fig. 9 is a STEM photograph of the entropy multifunctional super Vostian iron-based stainless steel in the present invention after being aged for 1 hour at 700°C and 800°C.

FIG. 10 is a STEM photograph of the entropy multifunctional super Vostian iron-based stainless steel in the present invention after aging at 800°C for a long time.

FIG. 11 is a graph showing the relationship between the stainless steel steel material of the present invention and the super-commercial super-iron field stainless steel S31254 held at an aging temperature of 700° C. for different periods of time and hardness.

Fig. 12 (a) Engineering stress-strain diagram and (b) work hardening rate of the commercial alloy S31254 and the entropy multifunctional super Vostian iron-based stainless steel of the present invention after annealing and aging at 700°C for 4 hours relation chart.

FIG. 13 is an image photograph of the entropy multifunctional super Vostian iron-based stainless steel of the present invention, which is subjected to a tensile test after aging and observes the distribution of the differential rows on the shear slip surface by STEM.

14 is a graph of cyclic polarization of commercial alloys 304SS, S31254 and the entropy multifunctional super Vostian iron-based stainless steel of the present invention and the properties after aging.

15 is a photograph of the antibacterial experiment results of commercial alloys 304SS, S31254 and the entropy multifunctional super Vostian iron stainless steel of the present invention after annealing and aging at different temperatures and times.

Please refer to FIG. 1. FIG. 1 is a phase diagram of a super-Wustfield iron-based stainless steel calculated by the thermodynamic analysis software-Thermal Calc simulation software. The present invention is based on a medium-entropy alloy design and uses Thermal Calc to simulate software Volume calculation to design different alloy composition, avoid the temperature range where sigma exists stably, and evaluate the lowest stable temperature where the high temperature stable phase FCC Vostian iron phase exists.

According to the calculation results, according to one of the preferred embodiments of the present invention, the entropy multi-functional super Vostian iron-based stainless steel whose composition contains up to 0.02wt.% carbon, 20.0~25.0wt.% chromium, 20.0~25.0wt. % Nickel, 4.0~6.0wt.% molybdenum, 0.0~5.0wt.% tungsten, 3.5~5.0wt.% copper, 0.0~1.0wt.% manganese, 0.2~0.3wt.% silicon, 0.3~0.5wt.% nitrogen , Balanced amount of iron and insignificant impurities.

The above-mentioned elements have different functions. In the present invention, in addition to carbon, chromium, nickel, molybdenum, manganese, and nitrogen as the main components, the remaining components can be selected according to actual needs. The effects of various components and their content ratios on the high-strength steel of the present invention will be described below:

Carbon: It is an important strengthening element in steel and the most effective element to strengthen steel. If the carbon content is too small, it is difficult to achieve the target strength. If the carbon content is too large, the hardening of the steel can be improved and it is easy to produce toughened iron or hemp iron , It may reduce the ability of plastic deformation, weldability, impact resistance and low temperature toughness. Therefore, the prior art reveals that the carbon content may be greater than 0 wt.% to 0.03 wt.% or less.

Chromium: an important element to improve the hardening energy of steel and improve corrosion resistance, if the chromium content is too low, the corrosion resistance may deteriorate, and if the chromium content is too large, it may increase the tendency of intermetallic compound precipitates, and cause Vostian iron phase is unstable. Therefore, the prior art reveals that the chromium content may be greater than 20wt.% to 24wt.%.

Nickel: It is one of the most important alloying elements in steel. It is not easy to form carbides with carbon. It can improve low temperature toughness and hardening energy when used in low alloy steel. It can also reduce the sensitivity of heat treatment changes and reduce the distortion and turtle quenching. crack. As a stable element of Vostian iron phase, and should be added in an appropriate amount to obtain the desired structure. The prior art reveals that the nickel content may be greater than 18wt.% to 23wt.%. Different from the prior art, the medium-entropy multi-functional super Vostian iron-based stainless steel disclosed by the present invention has a nickel content of 20.0-25.0wt.%.

Molybdenum: an element that can improve the corrosion resistance in chloride environments. If the molybdenum content is too low, corrosion resistance may deteriorate, and if the molybdenum content is too large, the amount of intermetallic precipitation may increase. The use of molybdenum with chromium, silicon and manganese can increase the strength, hardness and toughness of steel. The combination of molybdenum and chromium can improve the wear resistance of the surface layer and the toughness of the inner layer when the surface is hardened. Chromium-molybdenum steel has good ductility, weldability and deep hardening ability. The steel with coexistence of molybdenum and nickel has the properties of ductility, strength, machinability and deep hardness. The combination of molybdenum, nickel and chromium can produce excellent low alloy steel with high strength, high toughness and high hardening energy. Therefore, the prior art discloses that the molybdenum content may be 6.0 wt.% or more and 6.8 wt.% or less.

Manganese: It is an important solid solution strengthening element in steel and an effective element to strengthen the solidification of steel. It can be used to increase the strength of steel. If the content of manganese is too small, it may reduce the steel And may form coarse FeS, which may make the steel very fragile. If it is too large, the cost of the alloy may increase and the weldability may deteriorate, resulting in poor formability of the steel. Therefore, the prior art reveals that the manganese content can be greater than 0 wt.% to 0.6 wt.% or less.

Nitrogen: a solid solution strengthening element that can improve corrosion resistance, structural stability and material strength. If the nitrogen content is too low, physical properties such as corrosion resistance may deteriorate, and if the nitrogen content is too much, chromium nitride may be precipitated. Therefore, the prior art reveals that the nitrogen content may be greater than 0.19 wt.% to 0.30 wt.% or less. Different from the prior art, the mid-entropy multi-functional super Vostian iron-based stainless steel disclosed in the present invention has a nitrogen content of 0.3-0.5wt.%.

It should be emphasized that, unlike the prior art, according to the present invention, the entropy multi-function super-gas field iron-based stainless steel has a copper content higher than 3.0 wt.%, and even, the middle-entropy multi-function super-vos disclosed by the present invention The content of copper in the field iron stainless steel is as high as 3.5~5.0wt.

According to a preferred embodiment of the present invention, a method for manufacturing a medium-entropy multi-functional super Vostian iron-based stainless steel, first of all, prepare a raw material whose composition contains up to 0.02wt.% carbon, 20.0~25.0wt.% chromium, 20.0 ~25.0wt.% nickel, 4.0~6.0wt.% molybdenum, 0.0~5.0wt.% tungsten, 3.5~5.0wt.% copper, 0.0~1.0wt.% manganese, 0.2~0.3wt.% silicon, 0.3~0.5 wt.% nitrogen, balanced amount of iron, and insignificant impurities. The raw material composition is the alloy composition composition based on the medium entropy alloy design of the present invention and calculated using Thermal Calc simulation software.

Next, according to the method of the present invention, the raw material is subjected to a vacuum melting process to obtain a stainless steel with medium entropy and multi-functional super-Wastefield iron stainless steel.

In a specific embodiment, the vacuum melting process may be performed by vacuum induction melting method or vacuum arc melting method.

Next, the method according to the invention cools the stainless steel material. Finally, the method according to the present invention performs a homogenization process on the stainless steel ingot, so that the microstructure of the stainless steel steel is Vostian iron phase single-phase structure and no hard and brittle sigma phase remains.

According to the method of the present invention, a stainless steel steel material with a medium-entropy multifunctional super Vostian iron series stainless steel is manufactured. The manufacturing process, subsequent processing and testing will be described in detail below.

In a specific embodiment, the homogenization process can be achieved by placing the stainless steel material of the medium-entropy multifunctional super Vostian iron series stainless steel in a vacuum furnace at a homogenization temperature of 1200°C for 24 hours to achieve homogenization of the stainless steel material Change.

Further, according to the method of the present invention, at least one cold rolling process is performed on the stainless steel steel material at room temperature to obtain the finished steel material. Next, the method according to the present invention performs an annealing process on the finished rolled steel material, so that the finished rolled steel material has a grain size range of 19-320 μm.

In a specific embodiment, at least one cold rolling extension process can cold-roll the rolling amount of stainless steel Up to 80%. At least one cold rolling extension process can control the finish rolling temperature below Ar3 temperature (Ar3 temperature refers to the initial temperature of the high-temperature stable phase Vostian iron that begins to transform into ferrite iron during cooling, which can be measured by an expansion meter Or calculated by the formula) to obtain a finished rolled steel.

Further, according to the method of the present invention, an aging treatment process is performed on the finished rolled steel, resulting in precipitation of multiple copper-rich precipitates in the finished rolled steel. The particle size range of multiple copper-rich precipitates is 2~5nm.

The flow of smelting and subsequent processing and heat treatment performed by the above method according to the present invention is shown in FIG. 2.

Regarding the control of the sigma phase that is hard and brittle and harmful to mechanical properties, related prior art has been disclosed in U.S. Patent Publication No. 4,883,544. In order to suppress the precipitation of the sigma (sigma) phase during continuous casting, it is proposed Casting method with shaft crystal ratio controlled below 20%. U.S. Patent Publication No. 4,883,544 discloses that by simulating the phase equilibrium diagram, the temperature control can be avoided when the alloy is blended with the alloy composition to avoid precipitation of sigma (sigma) phase. Therefore, the stainless steel steel material obtained by performing the vacuum melting process according to the method of the present invention and not homogenized among the entropy multifunctional super Vostian iron-based stainless steels has a residual sigma phase. The metallographic photograph of the residual sigma phase and its composition analysis are shown in Figure 3.

The stainless steel materials obtained after smelting can be used in a vacuum furnace. The temperature was raised to 1200°C, and after 24 hours of homogenization, the residual sigma phase was removed. The X-ray diffraction pattern analysis results can be used to confirm whether there is residual sigma phase. The X-ray diffraction pattern analysis results of the entropy multifunctional super Vostian iron series stainless steel after homogenization in the present invention are shown in FIG. 4. From the face-centered cubic (FCC) single-phase Vostian iron substrate shown in FIG. 4, there is no sigma phase diffraction peak, which confirms the stainless steel steel of the entropy multifunctional super Vostian iron series stainless steel in the present invention After homogenization, no sigma phase remains.

In the present invention, the thickness reduction rate of the stainless steel steel with entropy multifunctional super Vostian iron series stainless steel in at least one cold rolling extension process can reach 80%, that is, the amount of cold working rolling can be as high as 80%. After cold rolling, the annealing temperature of the finished rolled steel of the present invention includes 950°C, 1000°C, 1050°C, 1100°C, 1150°C, and 1200°C. The annealing temperature includes 5min, 10min, 30min, and 60min. Annealing process. Annealing process of annealing temperature and different holding time, with the release of annealing, the cold-rolling process is used to plastically deform the stainless steel steel of the present invention to store energy in the finished steel, to control the size of the annealing recrystallized grains and then control the processing Mechanical strength. However, the annealing temperature must also be carefully controlled. If the annealing temperature is insufficient, it will still affect whether there is sigma precipitation in the single-phase FCC grains. After being homogenized, the stainless steel material of the present invention is cold rolled and annealed at 950°C for one hour. In the X-ray diffraction pattern analysis results, it can be found that the σ (sigma) phase remains in the Vostian iron base phase. The analysis results are shown in Figure 5. Therefore, continue to rise and fall The temperature of the fire reduces the residual sigma phase. The stainless steel material of the present invention is homogenized, cold rolled, and annealed at 1000°C for one hour. The image photograph observed with an electron backscatter diffraction analyzer (EBSD) is shown in FIG. 6. Figure 6 shows that the sigma phase remains at the grain boundary position of the base phase of the Vostian iron. Annealing at this temperature can find that most of the sigma (sigma) phase is heterogeneously precipitated out of the grain boundary of the Vostian iron phase, and some of them still exist. Within the grains of the Vostian iron phase, through EBSD observation and analysis, it was found that after homogenization, cold rolling and annealing at 1200°C, it can completely enter the single-phase FCC Vostian iron base phase without residual σ (sigma phase). The image photographs observed by EBSD are shown in Figure 7.

In a specific embodiment, the annealing temperature in the annealing process ranges from 1050 to 1200°C, and the holding time is between 5 min and 60 min. The annealing process can release part of the differential stress concentration accumulated by the finished steel after cold rolling, and the internal storage energy and the control of annealing temperature and time can be used to adjust the size of the recrystallized grains after annealing.

Although the σ(sigma) phase formation region can be crossed after annealing at a higher temperature, after the annealing temperature controls the metallography to be a single-phase FCC Vostian iron phase, the annealing temperature will be released along with the rolling process storage energy, which will affect the recrystallization crystal. The size of the grain size. Figure 8 shows the relationship between grain size and hardness after different annealing temperatures and times. The Hall-Petch equation reveals the relationship between the grain size and the material strength, and in Table 1 reveals the actual values of the grain size and material hardness at different annealing temperatures and times. Among them, the annealing temperature is 1200°C and the annealing time is 60 minutes. The large grain size is 281.2±34.9μm and the lower hardness is 182±5Hv. After annealing temperature 1050℃ and annealing time 5min, smaller grain size 216±3μm and higher hardness 21.3±2.0Hv can be obtained.

Table 1

After annealing, the finished rolled steel of the present invention can be strengthened by precipitation in the aging process, and the aging and holding time at different temperatures can be performed. The aging temperatures are 500 ℃, 600 ℃, 700 ℃, and 800 ℃, respectively, and the holding time is 0 ~9 hours, another observation with Scanning Transmission Electron Microscopy (STEM) shows that after aging temperature 700 ℃, 800 ℃ holding temperature for 1 hour, it can produce homogeneous precipitation of spherical copper-rich precipitation out of the iron phase grains of Vostian Objects, please see Figure 9. X-ray energy dispersive analyzer (EDS) analyzes the copper-rich precipitates, whose composition contains chromium-molybdenum-nickel-copper precipitates ranging in size from 2 to 20 nm. This copper-rich precipitate is beneficial to increase the strength. If the aging temperature is increased to 800 ℃, the holding time will be extended, and it will be found that the σ (sigma) phase of the precipitate along the crystal is not conducive to the tensile strength. After STEM-EDS mapping, the composition is rich in chromium and molybdenum, and the copper content is small. Of precipitates. After the aging temperature of 800°C is maintained for a long time, heterogeneous precipitation occurs on the grain boundary of the iron phase in Vostian to produce sigma precipitates. See the photograph of STEM observation images in Figure 10. FIG. 11 is a graph showing the relationship between the stainless steel steel material of the present invention and the super-commercial super-iron field stainless steel S31254 held at an aging temperature of 700° C. for different periods of time and hardness. The annealed stainless steel steel has a grain size between 19 and 320 μm . After aging at 700°C, the hardness increases with the aging time, and the highest peak hardness reaches 212Hv after 4 hours. The results shown in Fig. 11 confirm that the stainless steel of the present invention is superior to the commercial alloy S31254.

In addition, for face-centered cubic Vostian iron-based high-strength stainless steel, the behavior and mechanism of work strain hardening are closely related to the stacking energy during deformation. If the stacking fault energy (SFE) during deformation is greater than 35mJ/m ² , the work hardening mechanism is to use the differential row of lateral slip or differential row slip on the shear band (shear band) slip surface The method of shear band induced plasticity results in a work hardening strengthening mechanism. If the stack difference energy during deformation is less than 16mJ/m ² , the deformation mechanism will be accompanied by twin induced induced plasticity (TWIP) or phase change induced plasticity (TRIP) with lower stack difference energy. The mechanism produces work hardening. The energy of the main deformation mechanism of stainless steel is mainly determined by stack difference energy (SFE). The study found that the phase change induced plastic deformation effect mainly plays a role in low energy SFE steel (<20mJ/m ² ). The deformation behavior of medium-energy SFE steel (20-40mJ/m ² ) is characterized by the formation of nano-thin deformed twins in the deformed microstructure, which is the twinning-induced plastic deformation effect. A microband-induced plasticity hardening mechanism similar to the hardening mechanism of the Super Vostian iron-based stainless steel of the present invention has been reported in high energy SFE alloy (~90mJ/m ² ) related research. The mechanism of microstrip-induced plastic hardening is described by the formation of a thin planar shear zone, which is limited by the barrier barriers on both sides. The hardening mechanism leads to the refinement of the spacing of the various microstructures during strain, thus exhibiting high Realization of strain hardening rate.

In the present invention, the alloy design and fusion of the entropy multifunctional super Vostian iron series stainless steel is to use homogenization and rolling processing and select the annealing temperature to avoid falling into the sigma phase. The Vostian iron phase derived from the single-phase FCC The formation temperature in the. The invention controls the entropy multifunctional super Vostian iron series stainless steel. The grain size of the Vostian iron phase is between 20 and 310 μm , and uses the strengthening mechanism of shear band to induce plastic deformation, and it is aged at 800 ℃ at high temperature. During the precipitation process, copper-rich spherical precipitates were observed to be scattered out of the crystal grains. The size of the precipitate is 2~20nm, and its composition is iron: chromium: nickel: molybdenum: copper=21:20:20:4:17wt.%. The presence of copper-rich precipitates can also enhance the antibacterial ability of the entropy multifunctional super Vostian iron-based stainless steel in the present invention. Moreover, with the aging treatment for a longer period of time, it can be observed that in the present invention, the entropy multifunctional super Vostian iron-based stainless steel has a small amount of chromium-rich molybdenum phase strip-shaped heterogeneous precipitates precipitated on the grain boundaries, This is a heat treatment condition to be avoided.

In the present invention, the hardness, tensile yield stress, maximum tensile strength and elongation of the entropy multifunctional Vostian iron-based super stainless steel alloy after aging at 700℃ for 4 hours are better than that of the commercial alloy S31254. The tensile stress, maximum tensile strength and elongation can reach 212Hv, 344MPa and 757MPa respectively. The reason for this is that the stainless steel material of the present invention controls the contents of chromium, nickel, molybdenum and copper, and the use of strain hardening mechanism is based on the accumulation of differential stresses acting between the shear slip bands. The work strain hardening which is poorly arranged on the shear slip surface to form shear-induced plastic deformation is superior to traditional stainless steel. Different rows are arranged on the slip surface to form slip bands with different pitches. The slip bands with different pitches have stack energy of different energies. The stack energy determines the structure of stainless steel and the mechanism used for deformation. Its value is affected by the alloy. Influence of element content and deformation temperature. Taking the conventionally known high-manganese steel as an example, the Al content can significantly increase the stacking energy of the gas field in the steel and suppress the γ→ε transition. At present, the modified Olsen-Cohen thermodynamic model is often used to calculate the stack difference energy of the material, and the verified stack difference energy γ _SF calculation formula is obtained as follows:

γ _SF = 2 ρ △G _γ→ε +2 σ (1)

In equation (1), ρ is the atomic packing density of the closest packed surface of {111}, σ is the free energy of γ/ε phase interface, and △G _γ→ε is the difference of Gibbs free energy between γ _fcc →ε _hcp phases. The composition analysis shows that the Fe content in the Fe-Mn-Al steel is slightly higher than that in the Vostian iron structure, while the Mn content is slightly lower. Due to the high content of alloying elements in steel and the small volume fraction of ferrite iron structure, the compositional system of Fe-Mn-Al steel is used to estimate the stacking energy of the Vostian iron structure in the steel. According to the calculation formula of stack difference energy and the influence of each alloy element on Gibbs free energy, the △G _γ→ε and stack difference energy of Vostian iron at room temperature are 1150 and 86mJ/m ² , respectively, which is significantly higher than TRIP And TWIP steel. Conventional technology shows that when the stack difference energy is less than 20mJ/m ² , deformation easily induces plastic deformation of the Matian bulk, that is, the TRIP effect; when the stack difference energy is greater than 20mJ/m ² and less than 55mJ/m ² , deformation is easy to occur Induced twin crystal plastic deformation, that is, the TWIP effect; when the stack difference energy is greater than 55mJ/m ² , it is a differential row slip mechanism.

Taking the dual-phase Vostian iron and ferrite iron dual-phase lightweight high-strength steel as an example, the discontinuously distributed BCC ferrite iron structure did not undergo obvious plastic deformation, and the Vostian iron substrate deformed in the tensile direction, and there was no Matian loose phase transformation and mechanical twinning occurred. A large number of parallel slip bands are distributed in the Vostian iron grains, and part of the slip zone can pass through the annealed twins in the Vostian iron phase. The direction of the slip zone is twisted at the twins and maintains the same orientation on both sides. ,formed Stepped appearance. When the strain reaches a certain level, slip bands begin to appear in the Vostian iron grains, and gradually increase as the strain increases. The slip bands of different slip systems have slip band interactions in {111}, γ. This is due to the high three-dimensional mobility of the differential row of materials with high stack differential energy, which is prone to slip band interaction.

Fig. 12 is (a) engineering stress-strain diagram and (b) work hardening rate of commercial alloy S31254 and the entropy multifunctional super Vostian iron-based stainless steel of the present invention after annealing and aging at 700°C for 4 hours relation chart. In the present invention, the work hardening strengthening mechanism of the entropy multifunctional super Vostian iron-based stainless steel is accumulated by being poorly arranged on the sliding surface of the shear band to form an excellent shear-induced plastic deformation of work strain hardening. After annealing at 1200℃ for 1 hour and aging at 700℃ for 4 hours, it can obtain a yield strength of 344MPa, a maximum tensile strength of 757MPa, and an elongation of up to 53.9% after a tensile test, which is better than that of commercial alloy S31254. The strength is 314 MPa, the maximum tensile strength is 714 MPa, and the elongation is up to 55.5%, as shown in Table 2.

Table 2

FIG. 13 is an image photograph of the entropy multifunctional super Vostian iron-based stainless steel of the present invention, which is subjected to a tensile test after aging and observes the distribution of the differential rows on the shear slip surface by STEM. Fig. 13 shows the selective diffraction diagram. When the X-axis and Y-axis are tilted until the double-beam condition occurs, the g-vectors are -1-11, -3-11, -200, and 02-2, respectively. In the case of a shear-slip zone, this can form a reason for strong and high processing strain strengthening, so that the work hardening rate does not increase with the increase of the true strain Less. When the amount of strain is in the range of 4% to 24%, the work hardening will increase with the increase of the amount of strain, as shown in Figure 12.

In order to simulate the corrosive environment of seawater, the present invention uses 3.5wt% sodium chloride aqueous solution as a test solution to test the commercial alloy 304SS, S31254 and the entropy multifunctional super Vostian iron stainless steel of the present invention and the properties after aging The chip was subjected to cyclic polarization curve corrosion resistance evaluation. The results are shown in Figure 14. Important corrosion kinetic parameters such as corrosion potential (Corrosion potential, E _corr ), corrosion current density (Corrosion current density, I _corr ), and pitting potential (Pitting potential, E _p ) are summarized in Table 3.

table 3

From the results listed in Table 3, it can be found that the I _corr values of the commercial 304SS, S31254 and the super stainless steel of the present invention are not much different. At the same time, it can be noticed that the change in I _corr value after aging treatment is also very small, indicating that the current heat treatment parameters given have little effect on the corrosion rate of the substrate. Further, if the analysis can be found in commercial 304SS E _p having a lower value, meaning that its resistance to pitting from poor capacity numerical values of E _p. In contrast, E _p value of test strip gap through super stainless steels of the present invention after various aging the presentation of the commercial value of E _p S31254 very small. At the same time, the curve after the polarization potential retrace can be found. In addition to the positive hysteresis loop of the same size, the super stainless steel and the commercial S31254 of the present invention show the repassivation potential shown in the curve. , E _pp ) is also very similar, and the size of the (E _p -E _pp ) value in the table shows that the repassivation behavior and ability of the super stainless steel of the present invention is comparable to the commercial S31254. Regarding the corrosion resistance of copper-containing 316L stainless steel, the prior art [Tong Xi et.al., Materials science and engineering C 71, 2017 pp. 1079-1085] revealed the cyclic polarization curve results of copper-containing 316L stainless steel, from which we can see The (E _p -E _pp ) value of the copper-containing 316L stainless steel is 4 to 5 times that of the super stainless steel of the present invention and commercial S31254, indicating that the super stainless steel of the present invention has excellent corrosion resistance.

According to the conventional silver-rich alloy surface, the antibacterial mechanism of silver is electrostatic adsorption sterilization. Because silver ions are positively charged, they can be deformed due to the adsorption of negative charges such as -COOH-, -O-PO3-, and -S- on the cell walls and cell membranes of various bacteria, which changes the living environment of bacteria. The functions of proteins and proteases are blocked, destroying metabolic functions, causing physical perforation and rupture, causing cytoplasmic overflow, and causing bacterial death. The other sterilization mechanism is photocatalytic sterilization. Silver ions have the role of catalytic active centers. Under the action of light, they excite oxygen in the air or water to produce hydroxyl radicals and active oxygen ions. The active radicals or ionic energy produced by photocatalysis Destroy the proliferation ability of microbial cells, inhibit or kill bacteria.

Copper-containing antibacterial stainless steel is a small amount of copper added to the stainless steel, although in the early days there was It was added into the steel to increase corrosion resistance and workability, and its antibacterial properties were not used. The super stainless steel of the present invention was added with 3~5wt.% copper to make the particle size of the stainless steel 2~20nm. Precipitates of nano-level Cu evenly distributed in the base of Vostian iron. The antibacterial principle is similar to the electrostatic adsorption of silver ions. When copper metal ions are positively charged and contact with healthy bacteria, the copper positive ions and the negative on the bacterial cell wall The electric charge will attract each other to produce electrical neutralization, which causes the charge on the bacterial cell wall to weaken, making the bacterial cell wall weak, resulting in the outflow of bacterial tissue fluid and death. The photos of the antibacterial experiment results of the commercial alloy S31254 and the entropy multifunctional super Vostian iron series stainless steel of the present invention after annealing treatment and aging treatment (aging at 700°C for 4 hours) are shown in FIG. 15.

The antibacterial experiment carried out by the present invention adopts the plate coating method, the strain used is E. coli (E.coli ATCC 25922), cultivated by LB medium (Lysogeny broth), and its composition is 5 grams of yeast powder and 10 grams per liter of distilled water Pancreatin and 10 grams of sodium chloride. In the present invention, the surface of the experimental test piece made by the above alloy process is ground to a number of 1200, immersed in anhydrous alcohol and washed with an ultrasonic oscillator for 2 minutes, then air-dried and covered with aluminum foil paper. All antibacterial test items should be sterilized at 121°C and 27-30 psi for 20 minutes and dried in an oven at 50°C.

In the antibacterial experiment conducted by the present invention, E. coli was pre-incubated in a test tube with 2 mL LB for 24 hours at a concentration of about 109 CFU (colony-forming unit)/mL, and diluted with deionized water to a concentration of 8×10 ⁵ CFU/mL. 100μL of diluted bacteria was dropped on the test piece, and the test piece was placed in a micro pipette tip box. The outer part of the box was covered with cling film, and finally placed in the freshness box. The box was filled with a small amount of water to maintain 95% humidity. Incubate for 48 hours. After incubation, 50 μL of the bacterial solution was diluted 10 times, 50 μL of the suspension was applied to agar medium, and cultured at 37° C. and 95% humidity for 24 hours. Finally, the number of colonies was counted. The photograph shown in Fig. 15 is the result after 48 hours of cultivation of bacteria. The photos shown in Fig. 15 clearly confirm that the growth of the bacterial solution on the super stainless steel test piece is inhibited. In the present invention, the entropy multifunctional super Vostian iron-based stainless steel after annealing has a colony number equal to 96 (n=96) The number of colonies on the test piece of the entropy multifunctional super Vostian iron series stainless steel after annealing and aging treatment in the present invention is equal to 6 (n=6), which are far lower than the number of colonies on the test piece of commercial alloy S31254 (n =205). The antibacterial experiment conducted by the present invention confirms that the entropy multifunctional super Vostian iron-based stainless steel of the present invention has excellent antibacterial ability whether it is annealed or annealed and then aged.

Through the detailed description of the above preferred embodiments, it is believed that it can be clearly understood that according to the present invention, the entropy multifunctional super Vostian iron-based stainless steel has excellent machinability, mechanical properties, corrosion resistance, and antibacterial properties.

Through the above detailed description of the preferred embodiments, it is hoped that the features and spirit of the present invention can be described more clearly, rather than limiting the aspect of the present invention with the preferred embodiments disclosed above. On the contrary, the purpose is to cover various changes and equivalent arrangements within the scope of the patent scope of the present invention. Therefore, the scope of the patent scope applied for in the present invention should be interpreted broadly based on the above description, so that Cover all possible changes and equal arrangements.

Claims (10)

A medium-entropy multi-functional super Vostian iron series stainless steel, its composition includes: Up to 0.02wt.% carbon, 20.0~25.0wt.% chromium, 20.0~25.0wt.% nickel, 4.0~6.0wt.% molybdenum, 0.0~5.0wt.% tungsten, 3.5~5.0wt.% copper, 0.0~ 1.0wt.% manganese, 0.2~0.3wt.% silicon, 0.3~0.5wt.% nitrogen, balanced amount of iron and insignificant impurities. The middle-entropy multifunctional super Vostian iron series stainless steel as described in claim 1, wherein the middle-entropy multifunctional super Vostian iron series stainless steel undergoes a homogenization process, the middle-entropy multifunctional Super Vostian iron series stainless steel The microstructure of stainless steel is a Vostian iron phase single-phase structure and no hard and brittle sigma phase remains. As described in claim 2, the middle-entropy multifunctional super Vostian iron series stainless steel, wherein the middle-entropy multifunctional super Vostian iron series stainless steel precipitates many copper-rich precipitates after an aging process, the aging treatment One aging temperature range is 500~700℃, and one of the multiple copper-rich precipitates has a particle size range of 2~5nm. As described in claim 3, the middle-entropy multi-functional super Vostian iron series stainless steel, wherein the composition of the plurality of copper-rich precipitates is iron: chromium: nickel: molybdenum: copper=21:20:20:4:17wt. %. A method for manufacturing a medium-entropy multi-functional super Vostian iron series stainless steel includes the following steps: Prepare a raw material whose composition contains up to 0.02wt.% carbon, 20.0~25.0wt.% chromium, 20.0~25.0wt.% nickel, 4.0~6.0wt.% molybdenum, 0.0~5.0wt.% tungsten, 3.5~5.0 wt.% copper, 0.0~1.0wt.% manganese, 0.2~0.3wt.% silicon, 0.3~0.5wt.% nitrogen, balanced amount of iron and insignificant impurities; Performing a vacuum melting process on the raw material to obtain one of the medium-entropy multi-functional super Vostian stainless steels; Cooling the stainless steel; and A homogenization process is performed on the stainless steel ingot, so that the microstructure of the stainless steel material is a Vostian iron phase single-phase structure and no hard and brittle sigma phase remains. The method as described in claim 5 further includes the following steps: Under a room temperature environment, at least one cold rolling process is performed on the stainless steel to obtain a finished rolled steel, wherein the at least one cold rolling process is cold working rolling amount of one of the stainless steel materials is equal to or less than 80% ;as well as An annealing process is performed on the finished rolled steel, so that the finished rolled steel has a grain size ranging from 19 to 320 μm. The method according to claim 6, wherein one of the annealing processes has an annealing temperature of 1200°C, a first hardness of the finished steel is 184 Hv, a first yield strength of the finished steel is 319 MPa, and the finished steel One of the first tensile strength is 718MPa, the first elongation of the finished steel is 58.2%. The method according to claim 6, further comprising the following steps: An aging process is performed on the finished steel product, which results in precipitation of a plurality of copper-rich precipitates in the finished steel product, and a particle size range of one of the plurality of copper-rich precipitates is 2-5 nm. The method according to claim 8, wherein one of the aging treatments has an aging temperature of 700°C, one of the aging treatments has a process time of 4 hours, one of the finished steels has a second hardness of 212Hv, and one of the finished steels The second yield strength is 344 MPa, the second tensile strength of one of the finished steels is 757 MPa, and the second elongation of one of the finished steels is 53.9%. The method according to claim 8, wherein one of the aging treatments has an aging temperature of 700°C, one of the aging treatments has a process time of 8 hours, and one of the finished steels has a corrosion potential of -241.7mV. A corrosion current density is 0.27 μA/cm ² .

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